(a) Field of the Invention
The present invention relates to a wiring board (hereinafter also referred to as “semiconductor package”) for use in mounting an electronic component such as a semiconductor element. More particularly, it relates to a wiring board with switching function through which a signal communication is carried out between an electronic component mounted thereon and a motherboard (or a packaging board) such as a printed wiring board, and which is adapted to avoid a disadvantage which can possibly arise in the event of overheating of the electronic component, and relates to a method of manufacturing the same.
The wiring board with switching function according to the present invention is preferably applicable particularly in mounting electronic components which emit a large amount of heat, such as MPUs (microprocessor units), light emitting elements including LEDs (light emitting diodes), or the like, which are high in power consumption.
(b) Description of the Related Art
Generally, manufacturing of a semiconductor package such as BGA (ball grid array), LGA (land grid array) or PGA (pin grid array) involves preparing a core substrate used as a base material for the package; forming on both surfaces of the core substrate, a multilayer wiring structure, for example, by sequentially repeating a formation of a conductive pattern (a wiring layer), a formation of an insulating layer, and a formation of a via hole in the insulating layer; coating the outermost wiring layer with a protection film; and forming an opening at a desired position in the protection film to thereby expose a portion of the conductive pattern (i.e., a pad portion). Furthermore, in the case of BGA or PGA, a ball, a pin or the like serving as an external connection terminal is bonded to the exposed pad portion. Such a semiconductor package is configured to mount an electronic component (or a chip) such as a semiconductor element on one surface, and to be packaged on a motherboard such as a printed wiring board via the external connection terminal provided on the other surface. In other words, the chip and the motherboard are electrically connected with the semiconductor package interposed therebetween.
Thus, the semiconductor package is intended mainly to enlarge the pad pitch of the chip to that of the motherboard by rewiring between an electrode terminal of the chip mounted on the package and the external connection terminal (or the terminal for motherboard connection) of the package. In this respect, the semiconductor package is functionally the same as an interposer. Thus, the conventional semiconductor package basically functions as a medium for signal communication between the chip and the motherboard.
On the other hand, there is a semiconductor package which includes a package substrate having a function corresponding to a passive element (typically, a capacitance element) embedded therein. As a semiconductor chip or the like mounted on a recent package becomes more multifunctional, wirings routed in a package substrate become accordingly higher in density, and thus, wiring patterns are in closer proximity to each other, and a wiring length also becomes longer. The wiring patterns in close proximity to each other may cause a crosstalk noise or the like, and a long length of wiring may cause an increase in inductance and lead to a signal delay. As a result, a disadvantage such as a decrease in the processing speed of the electronic component mounted on the package, can possibly occur. In order to eliminate such a disadvantage, a capacitor function for achieving a desired decoupling effect is embedded in the substrate.
As can be seen with respect to the conventional semiconductor package, only the package including the passive element which achieves a specific effect besides the signal communication medium function, has been put into practical use, and no other special function has been included in the package. Thus, a function corresponding to a switch element, a filter element, or the like, is generally mounted on the motherboard as an external component.
An example of technology related to the above-mentioned art is disclosed in Japanese examined Utility Model Publication (JUMP) (Kokoku) 7-26824. This publication discloses a hybrid integration device having a switching element. The device includes a double-sided printed wiring board having a control element mounted on one surface and metal foil remaining on the other surface, and a metal-base printed wiring board having a switching element mounted on one surface. In this configuration, the printed wiring boards are disposed face to face so that the elements mounted on the wiring boards face each other, and a terminal portion having a ring-shaped saturable inductance element is provided at one end of a gap formed by the printed wiring boards facing each other. Further, the other end of the gap is covered with a metal plate, and a connection lead is drawn out through the ring-shaped saturable inductance element.
As mentioned above, with respect to the conventional semiconductor package (or wiring substrate), only the package including the passive element which achieves a specific effect besides the signal communication medium function has been put into practical use. Thus, a function corresponding to a switch element, a filter element or the like, is generally mounted on the motherboard as an external component. This leads to an increase in the number of components on the motherboard, which in turn, causes a problem in that the area occupied by the external components increases the size and cost of the semiconductor package.
On the other hand, when an electronic component high in power consumption (or large in the amount of heat emitted), such as MPU, is mounted, overheating may possibly occur during operation of the component and thus cause malfunction, thermal runaway or the like. In this case, provision of a function corresponding to a fuse or the like for preventing such a trouble with the package would be effective.